Yes, children or full-time college students with unearned income of greater than $1,300 need to file a return, because of "kiddie tax."
Typically, the first $1,300 worth of a child's unearned income isn't taxed, the next $1,300 is taxed at the child's rate, and anything above $2,600 is taxed at the parent's rate. This is calculated on Form 8615.
See: What is IRS Form 8615: Tax for Certain Children Who Have Unearned Income for more information.